The invention relates to speed-responsive electrical systems and circuit arrangements and more specifically to such systems and circuit arrangements responsive to the speed of a vehicle, such as a road vehicle, and, for example, for automatically controlling the speed of the vehicle.
Automatic speed control systems are known by which the driver may select a desired speed for the vehicle and the system thereafter automatically adjusts the engine power so as to tend to keep the vehicle speed at the desired value.
However, known systems have a disadvantageous effect when a vehicle descends a slope particularly if the downhill slope is followed by an uphill section. When a vehicle under control of such a system descends a hill, the vehicle will accelerate and its speed will become well in excess of the desired speed value. During this process, therefore, the system will reduce the engine power to a minimum. If the downhill stretch of road is followed by an uphill section, then the vehicle speed will fall as the vehicle begins to run uphill, but the system will not begin to increase the engine power from its minimum setting until the actual speed has fallen to the value represented by the desired speed value. Therefore, a large amount of the momentum gained by the vehicle in running downhill will be lost. This is particularly disadvantageous when the vehicle is a heavy vehicle, a truck for example.
An object of the invention is to provide an improved automatic vehicle speed control system.
A more specific object of the invention is to provide an automatic vehicle speed control system which helps to avoid loss of the kinetic energy gained when the vehicle runs downhill.